1. Field of the Invention
The present invention relates to an apparatus for and a method of erasing a residual radiation image from a stimulable phosphor panel by applying erasing light to the stimulable phosphor panel after a radiation image has been read from the stimulable phosphor panel by applying stimulating light to the stimulable phosphor panel.
2. Description of the Related Art
There has heretofore been known a stimulable phosphor which, when exposed to radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet radiation, or the like), stores part of the energy of the radiation, and, when subsequently exposed to stimulating rays such as visible light, emits light in proportion to the stored energy of the radiation.
A radiation image information recording and reproducing system, which has been developed in the art, temporarily records a radiation image of a subject such as a human body on a stimulable phosphor panel having a stimulable phosphor layer. Thereafter, the radiation image information recording and reproducing system applies stimulating light such as a laser beam or the like to the stimulable phosphor panel to emit light representative of the recorded radiation image, and then outputs the radiation image as a visible image on a recording medium such as a photosensitive medium or the like or a display unit such as a CRT or the like, based on an image signal that is generated by photoelectrically reading the light emitted from the stimulable phosphor panel. After the radiation image has been read from the stimulable phosphor panel, the stimulable phosphor panel is irradiated with erasing light to erase any remaining radiation image therefrom, and then used again for recording a radiation image thereon.
If erasing light exclusive of ultraviolet radiation is used to erase the remaining radiation image from the stimulable phosphor panel, then electrons trapped in a deep layer where they cannot be removed by visible erasing light tend to remain unremoved. Conversely, if erasing light including much ultraviolet radiation is used, then though those trapped electrons can be removed from the deep layer, new trapped electrons are generated by the ultraviolet-rich erasing light itself.
In view of the above drawback, there has been developed a technology for efficiently erasing remaining radiation image information from a stimulable phosphor panel by applying first erasing light including a radiation in an ultraviolet wavelength range to the stimulable phosphor panel to remove trapped electrons from the deep layer region and thereafter applying second erasing light in a wavelength range other than the ultraviolet wavelength range to remove trapped electron that have newly been generated in a rather shallow layer by the first erasing light (see Japanese Laid-Open Patent Publication No. 5-119412).
The dose of radiation applied to the stimulable phosphor panel differs depending on the imaging conditions, the region of the subject that is to be imaged, etc. Therefore, the amount of remaining radiation energy differs depending on the position on the stimulable phosphor panel. Furthermore, stimulable phosphor panels for use in imaging subjects are available in various sizes depending on the purpose for which the image is captured.
If the level of erasing energy for erasing remaining radiation image information is established based on the maximum level of radiation energy that is stored in the stimulable phosphor panel and the remaining radiation image information is erased with the established level of erasing energy, then the remaining radiation image information can reliably be removed from the stimulable phosphor panel.
With such an erasing energy level setting, however, more erasing energy than necessary is applied to those areas of the stimulable phosphor panel where the maximum level of radiation energy is not stored. As a result, the erasing process tends to result in a wasteful consumption of electric energy. If the level of erasing energy is established based on the maximum stimulable phosphor panel size regardless of different stimulable phosphor panel sizes that are actually used, then some erasing energy is also wasted.